Recently, as a semiconductor wafer (hereinafter, simply referred to as a “wafer”), on which semiconductor devices is to be formed, is scaled up, it has been required to manufacture semiconductor devices even on a peripheral region of the wafer W, e.g., on a range within about 10 mm from an edge of the wafer toward a center thereof. Usually, a temperature distribution of the wafer affects a distribution of radicals in plasma by which a plasma process is performed on the wafer. Thus, in order to perform a uniform plasma process on the entire region of the wafer, the temperature of the peripheral region of the wafer needs to be controlled to be substantially the same as the temperature of the other region of the wafer. For the purpose, conventionally, there has been developed a technique for controlling the temperature of the focus ring to cool the focus ring in order to reduce radiant heat from the focus ring.
However, if the entire wafer temperature becomes lower as the focus ring is cooled, a resist film coated on the wafer as a pattern mask is easily etched by the plasma. Thus, in order to prevent a great decrease of the entire wafer temperature, the present applicant has developed a technique in which a first focus ring (hereinafter, referred to as an “inner focus ring”) is provided and a second focus ring (hereinafter, referred to as an “outer focus ring”) is placed at an outside of the first focus ring, and the first focus ring is cooled whereas the outer focus ring is not cooled but it is rather heated (see, for example, Patent Document 1).
Patent Document 1: Japanese Patent Application No. 2010-021079
Generally, in a gap between two members having greatly different temperatures, deposits are likely to adhere to a member having a lower temperature. Actually, the present inventor has found out that, when the aforementioned so-called dual focus ring including the inner focus ring and the outer focus ring is used, deposits tends to easily adhere to the inner focus ring in a gap between the inner and outer focus rings.
Since the gap between the inner focus ring and the outer focus ring is narrow and the plasma cannot be introduced into the gap easily, it is difficult to remove the deposits adhering to the inner focus ring by aching or the like. Thus, in order to remove the deposits from the inner focus ring, it is required that a chamber is opened to the atmosphere and the inner focus ring is taken out. As a result, an operation rate of a substrate processing apparatus including the focus ring would be deteriorated.
Further, in the substrate processing apparatus, a susceptor on which the inner focus ring or the outer focus ring are mounted is cooled to a temperature lower than the temperature of the inner focus ring. Accordingly, a temperature difference between the inner focus ring and the susceptor is increased. As a result, deposits adhere to the susceptor in a gap between the inner focus ring and the susceptor.
Since the gap between the focus ring and the susceptor is also narrow, in order to remove the deposits from the susceptor, it is required the chamber is opened to the atmosphere and the inner focus ring is taken out to expose the susceptor. As a result, the operation rate of the substrate processing apparatus would be also deteriorated.